1. Field of the Invention
The present invention relates to an electric power steering apparatus equipped with an electric motor for outputting assist torque to the steering wheel of a vehicle, and a control unit for controlling the driving of the electric motor.
2. Description of the Related Art
In the past, there has been known an electric power steering apparatus which is equipped with an electric motor for outputting assist torque to the steering wheel of a vehicle, and a control unit mounted on the electric motor for controlling the driving of the electric motor.
For example, in an electric power steering apparatus disclosed in a first patent document (Japanese patent No. 3,638,269), a metal substrate on which a bridge circuit comprising semiconductor switching elements for switching a current supplied to an electric motor is mounted, and a high current board having a conductive plate, a motor terminal and so on insert molded into an insulating resin are electrically connected to each other via a connecting member. Here, the connecting member is fixedly attached onto, and then soldered to, the metal substrate, and at the same time is electrically connected through welding with the conductive plate and the motor terminal of the high current board.
In addition, in a second patent document (Japanese patent application laid-open No. H7-297576), there is disclosed an arrangement in which a terminal having its one end embedded in a resin case that receives a circuit board and a leading terminal arranged on circuit wiring of the circuit board are connected with each other by a lead segment, and the terminal and the lead segment connected with the leading terminal are connected with deriving the terminal are connected with each other by laser welding is disclosed.
In the electric power steering apparatus as described in the above-mentioned first patent document, there is the following problem. That is, the connecting member is fixedly attached onto the metal substrate so as to prevent the connecting member from floating upon soldering thereof, and hence a sufficient area of the metal substrate is required for arrangement and tightening operation of screws for the attachment of the connecting member. In addition, an impact force generated when the connecting member is fixed onto the metal substrate is transmitted to the component parts of the bridge circuit before soldering thereof onto the metal substrate, so there occur positional shifts of such component parts.
Further, in the second patent document, the lead segment is connected with the circuit wiring of the circuit board via the leading terminal. As a result, there arises a problem that the apparatus becomes large in size, increased in the number of component parts and hence high in cost, as well as low in reliability of soldered connections of the parts mounted on the metal substrate.